Paul Whelan, an ex-cop and retired Marine who now works as a global security director for a Michigan-based auto parts supplier, disappeared in Moscow over the weekend.

His twin brother, David, said Paul was in Russia for the wedding of a Marine friend, but lost contact Dec. 28, “which was very much out of character for him even when he was traveling.”

On Monday, Russia’s main security agency, the FSB, confirmed it had detained Whelan while he was “carrying out spying activities” — and offered no further explanation, let alone evidence.

Former US diplomatic and security officials say the arrest looks like Putin’s revenge for the US prosecution of Maria Butina, who two weeks ago pleaded guilty to serving as a Russian agent during the 2016 presidential campaign.

American consular officials finally got to meet with Whelan on Wednesday, days after the time required under the Geneva Convention. Secretary of State Mike Pompeo vows to “demand his immediate return” unless Moscow can somehow provide proof of its (absurd) charges.

The Trump administration should make it clear to Putin & Co. that Washington won’t play the hostage game: If they don’t release Whelan swiftly, Moscow must suffer consequences.